Porous non-friable polymer film

ABSTRACT

Porous films are provided which include a blend of a film forming polymer and a non-film forming material, the film having a network of pores or channels throughout the film. The porous polymer films are formed between 0° and 80° C. retain porosity at elevated temperatures and are non-friable. A process for preparing porous polymer films and their applications are disclosed.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

This is a non-provisional application of prior pending U.S. provisionalapplication serial No. 60/241,603 filed Oct. 19, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the production of porous non-friablefilms from emulsion polymers, porous films formed at ambient temperatureand processes of manufacturing films having permanent porosity.

2. Description of the Related Art

It is well known that latex films containing particles that are wellordered prior to the final stage of film formation exhibit the bestbarrier properties. When latex films are used as binders, the samebarrier properties can be a disadvantage where access to reactive oradsorptive sites is required. Therefore, latex films having porousstructures or transport pores are desirable would have utility inchemical and biochemical processes, such as those that utilize liquidbarrier technology, breathable coatings, supported catalysts, sensortechnology, encapsulated biocides, immobilized bacteria technology orimmobilized cell technology.

A number of different techniques have been employed to create porousfilms by deliberate reductions in latex stability prior to filmformation and by exceeding critical pigment volume fractions, the latterinvolves adding excess pigment or filler so that there is enough binderto glue the particles together yet not enough to completely fillinterstitial voids, but each technique has serious drawbacks, namely,the inability to control and retain a pore structure in the film.

Compositions derived from an intimate mixture of an aqueous latex of afilm forming or coating polymer and the cells of an organism have beendisclosed in a European publication, EP 0 288,203 B1. The polymer hassufficient fluidity to undergo at least partial coalescence and aprocess for the production of an enzyme reaction product, formed bymixing the polymer, bacterial cells and a flocculant, causing the cellsand the polymer to agglomerate. One important aspect of the processdisclosed is the use of polymer flocculation to produce the porouspolymer/bacteria agglomerates. This aspect limits the general utility ofthe process by requiring a second ingredient be added or some othertrigger be used at the point of creating the porous agglomerates. Asecond aspect of this disclosure is the need to anneal the latexparticles at a temperature above the Tg of the polymer. If the operatingtemperature of the porous agglomerates is at or above room temperaturethen the latex particle must be annealed substantially above roomtemperature. If the particles could be annealed at room temperature thenthe porous agglomerates would quickly lose porosity at room temperature.Another important limitation of the disclosure in EP 0 288,203 B1 is theinability of the porous agglomerates to function at high operatingtemperatures (T˜80° C.), due to continued particle coalescence. Polymershaving relatively high Tg (>80° C.) in such a process, however, wouldrequire annealing at temperatures well above 80° C. to achievesufficient fluidity, a condition which would be detrimental to thebacteria or other organisms. The additional requirement of relativelyhigh operating temperatures has become more important as bio-processingtechnology has focused on thermophilic bacteria, which are capable ofsurviving at 80° C. for extended periods of time. It is clear that aprocess for forming smooth, porous films at ambient temperature, whichare a capable of withstanding high operating temperatures without theconcomitant loss of porosity is highly desirable, yet is not possiblegiven the disclosure of EP 0 288,203 B1.

Another process for preparing porous composite membranes forultrafiltration and micro-filtration membranes has been disclosed inEuropean publication, EP 0 711,199 B1. The membranes are prepared bydepositing discrete, spherical, polymeric particles, obtained bysuspension, dispersion or emulsion polymerization on the surface of aporous substrate to obtain the composite and using thermal coalescenceof the particles or chemical means to stabilize the resulting composite.A key limitation of the disclosure in EP 0 711,199 B1 is the need tothermally coalesce the latex particles at relatively high temperatures(>120° C.). There are many applications, including bacteria/latexcomposite films, in which the high annealing temperature is notpractical. A number of typical processing and performance limitationsassociated with this membrane technology, such as the restricted choicesof available pore sizes, has been detailed in a publication of Jons,Ries and McDonald in the Journal of Membrane Science, Vol. 155, pages79-99 (1999). Thus, an enabling process to form porous films comprisinglatex particles at ambient temperature would indeed have significantutility.

Current aqueous latex polymer technology utilizes the process of latexfilm formation to afford continuous, non-porous films. In a number ofimportant chemical and biochemical processes, however, polymer filmsthat retain a high degree of porosity so as to allow small molecules todiffuse, relatively unhindered, in and out of the film are of greatcommercial utility. It is also desirable in such applications that filmformation be accomplished at or close to ambient temperature and theresulting porous film not be friable after film formation is complete. Along recognized problem has been to make a permanently porous film fromwater-borne latex dispersion polymers, such that film formation occursat ambient temperature and the resulting film once formed is notfriable, possesses a high degree of porosity and retains porosity atelevated temperatures for long periods of time. Currently aqueous latextechnology either affords films with no porosity, partially coalescedfilms that are non-uniform and have stability issues, films with highporosity which require elevated temperature for film formation, or filmshaving high porosity which require polymer flocculation to create theporous structure.

SUMMARY OF THE INVENTION

Inventors have discovered a process to create permanent porosity inpolymeric films. By employing such a process, inventors have producedporous polymer films at ambient temperatures, polymer films that have apermanent pore structure and polymer films that retain porosity atelevated temperatures. The present invention discloses three aspects tosolving the current problem of producing permanently porous polymerfilms. The first aspect involves blending a non-film forming material inparticulate form and film forming latex polymer particles havingdiameters small enough to fit through the interstices formed from thenon-film forming particle matrix. The second aspect involves using acore-shell latex polymer such that the inner core of the polymerparticle is a non-film forming polymer and the shell is a film formingpolymer particle. The third aspect involves using large dimension,emulsion polymer particles. The present invention also contemplatesusing blends of all polymer types disclosed in the above mentionedaspects of the invention. The porous polymer films of the presentinvention provide improved adsorbent performance and the potential forsustained release of reaction products from entrapped organisms orimmobilized cells.

DETAILED DESCRIPTION OF THE INVENTION

According to the first aspect of the invention there is provided aporous film comprising a blend of (a) at least one non-film formingmaterial and (b) at least one film forming polymer, the film having anetwork of pores or channels throughout the film, wherein the filmforming polymer is present in the blend from between 5 and 35%, based onthe total volume of polymer and the film is non-friable.

According to the second aspect of the invention there is provided aporous film comprising a water-borne latex dispersion of a multi-stagepolymer having at least one non-film forming material and at least onefilm forming polymer, the porous film maintains porosity up to 160° C.,wherein the film forming polymer has a Tg no greater than 20° C., thenon-film forming material is a polymer having a Tg of at least 30° C.,wherein the film forming polymer is present in the blend from between 5and 35%, based on the total volume and the film is non-friable.

According to all aspects of the invention there is provided a processfor producing porous films comprising the steps of depositing acomposition of the first three aspects of the invention alone or incombination in a liquid state on a substrate and evaporating a carriermedium below 100° C.

The porous films usefully employed in accordance with the inventionretain porosity after film formation and are essentially non-friable.The present invention additionally provides porous polymer films,whereby film formation occurs between 0° and 80° C. and porous polymerfilms that retain porosity up to 160° C.

The present invention provides a general process for the production ofporous films between 0° and 80° C., porous films that retain porosityafter film formation, and porous films that are non-friable. The presentinvention also provides a process for preparing porous films thatmaintain porosity at elevated temperatures. In a specific application ofthe process, the porous film entraps chemical compositions or biologicalspecies. The process provides thin films that are smooth and uniform,and formed using traditional coating techniques.

The present invention provides porous polymeric films having adistribution of open pores ranging from at least 1 nm to 5 μm indiameter. The invention provides porous, polymeric films that areamenable to use in fluidized bed reactors, packed bed reactors, spiralwound flow through reactors, or plate and frame flow through reactors.The invention contemplates a porous polymeric biological-support whichis inexpensive and easily processed. Biocatalytic films containingimmobilized organisms and cells can be prepared according to any aspectsof the present invention. Polymer films prepared according to thepresent invention have and retain porosity in the dry state. The numberand distribution of pores retained depend on a number of film processingvariables, such as drying and casting.

A “porous film” herein is defined as a polymer film having a network ofpores or channels throughout the film. Porosity refers to an open porestructure throughout the film. The network of pores may be continuousand has desirable transport properties.

A “film forming” polymer herein is defined as a polymer having a glasstransition temperature less than 20° C., preferably less than −10° C.,as measured by differential scanning calorimetry (DSC), most preferablybelow −20° C. By virtue of the low glass transition temperature, filmsprepared from such polymer particles typically will not form porousfilms when film formation occurs at temperatures greater than 20° C.

A “non-film forming material” herein is a polymeric or an inorganiccomposition.

A “non-film forming polymer” herein is defined as a polymer having aglass transition temperature greater than 20° C., and preferably greaterthan 80° C., and more preferably greater than 100° C., as measured bydifferential scanning calorimetry (DSC).

Inorganic compositions refer to any inorganic solids, namely, silicates,alumino-silicates, metal carbonates such as calcium carbonate, or metaloxides such as zinc oxide, or titanium dioxide, preferably in the formof solid particles.

Polymeric compositions refer to compositions formed as polymerizationproducts of organic monomers, preferably in the form of emulsion polymerparticles, large dimension emulsion polymer particles, macroreticularresins, or colloidal particles.

Film formation herein is defined as the process of evaporation of aliquid carrier (which may or may not be a solvent) from a fluidsuspension of particles resulting in a transition from a fluidsuspension of particles to a solid film.

A “non-friable film” herein is defined as a film which resists abrasion.The friability of a film is determined using a simple finger abrasiontest, involving rubbing the film with a finger and examining forevidence of mechanical deterioration.

A “waterborne latex composition” herein is defined as a latexcomposition containing a medium that evaporates on drying which ispredominantly water, yet may contain a water-miscible solvent such as,for example, alcohols, ethylene glycol ethers, and propylene glycolethers. Preferably, the porous films are prepared from compositionscontaining water-borne, dispersion polymer particles.

Large dimension particles herein are defined as water-borne latexpolymer compositions which have an aspect ratio greater than 1. Suchcompositions are referred to as rods and filaments.

Porous films of the present invention are prepared from compositionscontaining a blend of non-film forming materials and film formingpolymer particles, such that the volume fraction of film forming polymeris between 5% and 35% based upon the total volume of the solids. Thediameter of the film forming particles should be 20% or less in sizethan the largest dimension of the non-film forming material. It ispreferred but not required that the non-film forming material is awater-borne latex polymer composition.

A porous film of the present invention is also prepared from polymerparticles made by sequential polymerization techniques such that thedispersion polymer particle contains a non-film forming material and afilm forming polymer, wherein the film forming polymer is between 5% and35% based on the total volume of the particle. It is preferred that thenon-film forming material is a water-borne latex polymer composition.

A porous film is prepared as well, in accordance with the presentinvention, from non-spherical, (i.e. rods and filaments) non-filmforming emulsion polymer particles. Optionally, a film forming polymermay be added to the composition to help stabilize the resulting polymerfilm.

In addition, porous films of the present invention are prepared fromblends of any or all of the compositions described above.

Polymer particles can be prepared from free radical additionpolymerization or condensation polymerization. In a preferredembodiment, the film forming and non-film forming polymer particles areprepared using techniques well known in the art to prepare dispersion,suspension or emulsion-polymerized addition polymers. Conventionalsurfactants may be used such as, for example, anionic and/or nonionicemulsifiers such as, for example, alkali metal or ammonium alkylsulfates, alkyl sulfonic acids, fatty acids, and oxyethylated alkylphenols. The amount of surfactant used is usually 0.1% to 6% by weight,based on the weight of total monomer. Either thermal or redox initiationprocesses may be used. Conventional free radical initiators may be usedsuch as, for example, hydrogen peroxide, t-butyl hydroperoxide, ammoniumand/or alkali persulfates, typically at a level of 0.05% to 3.0% byweight, based on the weight of total monomer. Redox systems using thesame initiators coupled with a suitable reductant such as, for example,isoascorbic acid and sodium bisulfite may be used at similar levels.

The average particle diameter of the polymer particles which can beusefully employed in accordance with the invention ranges from 20nanometers to 10000 nanometers. The diameter of the polymer particlesmay be controlled by the amount of conventional surfactants added duringthe polymerization process. It is known in the art that by increasingthe amount of surfactant added during polymerization, the diameter ofthe polymer particles can be reduced and by reducing the amount ofsurfactant, one can increase the diameter of the polymer particles.Particle sizes from 20 to 10000 nanometers are achieved by adding from6% to 0.1% surfactant by weight, based on the weight of total monomer,respectively. Conventional surfactants include anionic, nonionicemulsifiers or their combination. Typical anionic emulsifiers includealkali or ammonium alkyl sulfates, alkyl sulfonic acids, and fattyacids. Typical non-ionic emulsifiers include polyoxyethylated alkylphenols, alkyl phenol ethoxylates, polyoxyethylated straight-chainalcohol, amine polyglycol condensate, modified polyethoxy adducts,polyoxyethylated mercaptans, long chain carboxylic acid esters, modifiedterminated alkylaryl ether, and alkyl polyether alcohols.

Methods for preparing large uniform non-film forming single ormulti-stage polymers (between 1000 nm and 10000 nm) are disclosed patentU.S. Pat. No. 5,147,937 and can be usefully employed in accordance withthe invention.

The addition polymer particles are preferably copolymers of at least oneethylenically unsaturated monomer, such as, for example, acrylic estermonomers including methyl acrylate, ethyl acrylate, butyl acrylate,2-ethylhexyl acrylate, decyl acrylate, methyl methacrylate, butylmethacrylate, lauryl (meth)acrylate, isobornyl (meth)acrylate, isodecyl(meth)acrylate, oleyl (meth)acrylate, palmityl (meth)acrylate, stearyl(meth)acrylate, hydroxyethyl (meth)acrylate, and hydroxypropyl(meth)acrylate; acrylamide or substituted acryl amides; styrene orsubstituted styrenes; butadiene; ethylene; vinyl acetate or other vinylesters; vinyl monomers, such as, for example, vinyl chloride, vinylidenechloride, N-vinyl pyrrolidone; amino monomers, such as, for example,N,N′-dimethylamino (meth)acrylate; and acrylonitrile ormethacrylonitrile. Additionally, copolymerizableethylenically-unsaturated acid monomers in the range of, for example,0.1% to 10%, by weight based on the weight of the emulsion-polymerizedpolymer, acrylic acid, methacrylic acid, crotonic acid, itaconic acid,fumaric acid, maleic acid, mono methyl itaconate, mono methyl fumarate,monobutyl fumarate, maleic anhydride,2-acrylamido-2-methyl-1-propanesulfonic acid, sodium vinyl sulfonate,and phosphoethyl methacrylate, may be used.

Chain transfer agents, such as, for example, mercaptans may be used inan amount effective to provide a GPC weight average molecular weight of10,000 to 1000,000. “GPC weight average molecular weight” means theweight average molecular weight determined by gel permeationchromatography (GPC) described on page 4, Chapter 1 of TheCharacterization of Polymers published by Rohm and Haas Company,Philadelphia, Pa. in 1976, utilizing polymethyl methacrylate as thestandard.

With regard to the first aspect of the invention, the non-film formingmaterial may be a hollow polymer particle prepared as described in U.S.Pat. No. 4,427,836. By making the non-film forming polymer hollow, asignificant reduction in film density can be achieved. The non-filmforming material may include a polymer shell as an encapsulant foranother material such as a biocide, a pharmaceutical compound, anutrient for living organisms, a herbicide, a plant growth regulator, afungicide, an anti-mildew agent, a fragrance, camphor, sanitizers, skinconditioner oils, UV screens, insecticides, insect repellents, or airfresheners. Methods for making such particles are disclosed in U.S. Pat.No. 5,972,363.

In another aspect of the invention, the film forming or non-film formingpolymer particles can be prepared using techniques well known in the artto prepare dispersed condensation polymers. The processes often involvethe synthesis of a polymer or pre-polymer in an organic solvent orpolymer melt, with subsequent inversion into water with potential chainextension occurring after inversion. Preferred are polyurethanedispersion polymers. These polyurethane dispersion (PUD) compositionsare desirable due to their advantageous properties such as good chemicalresistance, abrasion-resistance, toughness, elasticity and durability. Atypical waterborne PUD is a poly (urethane-urea) which contains bothurethane and urea groups.

The polyurethane polymer particles are made by the well known reactionbetween polyols and polyisocyanates to give isocyanate terminatedpre-polymers. These pre-polymers are then dispersed into an aqueousmedium. Diamine and triamines are often added to the aqueous dispersionof the pre-polymer to react with the remaining isocyanate groups forincreasing the molecular weight of the polymer particles and forincorporating more urea groups in the polymer chain. After dispersionthe remaining isocyanate groups in the pre-polymer can also react withwater to yield an amine. These amines will also react with isocyanategroups to chain extend the pre-polymer. The polyols used to prepare PUDscan be either linear or branched polyethers, polyesters, orpolycarbonate polyols. Low molecular weight diols and triols are oftenused in conjunction with the higher molecular weight polyols to adjustthe amount of urethane content and branching in the PUD. The lowmolecular weight polyols can also contain acid (for example carboxyl orsulfonic acid) groups or amine groups which can aid in the dispersionand stabilization of the PUD. The polyisocyanate can be any aliphatic,cycloaliphatic or aromatic multifunctional isocyanate. The chainextenders can be any multifunctional amine, hydrazine, multifunctionalhydrazine or hydrazide. Optionally internal emulsifiers may be added tothe pre-polymer for aiding in the dispersion of the pre-polymer into theaqueous medium. The internal emulsifiers include diol or diamines thatcontain ionic groups, such as, carboxyl or sulfonate; multifunctionalisocyanates that contain these ionic groups; nonionic hydrophilicpolymer segments, such as, polyoxyethylene diols; or dials and diaminesthat contain these nonionic hydrophilic polymer segments.

Polyurethane particle size can be controlled during the dispersion stageby a combination of shear forces generated during the dispersion stage,viscosity of the pre-polymer, the temperature of the aqueous dispersingmedium and acid or amine groups and internal emulsifiers in thepre-polymer. The particle size is decreased by:

1. increasing the level of acid or amine groups;

2. increasing the internal emulsifiers in the pre-polymer;

3. increasing the shear forces generated during the dispersion stage;

4. increasing the temperature of the aqueous dispersing medium; or

5. decreasing the viscosity of the prepolymer.

The particle size is increased by reversing the factors described above.

With regard to the second aspect of the present invention, theemulsion-polymerized addition polymer is prepared by a multistageemulsion addition polymerization process, in which at least two stagesdiffering in composition are formed in sequential fashion. Such aprocess usually results in the formation of at least two mutuallyincompatible polymer compositions, thereby resulting in the formation ofat least two phases. The mutual incompatibility of two polymercompositions and the resultant multiphase structure of the polymerparticles may be determined in various ways known in the art. The use ofscanning electron microscopy using staining techniques to emphasize thedifference between the appearance of the phases, for example, is such atechnique. Such particles are composed of two or more phases of variousgeometries such as, for example, core/shell or core/sheath particles,core/shell particles with shell phases incompletely encapsulating thecore, core/shell particles with a multiplicity of cores,interpenetrating network particles and multi-lobed particles describedin the commonly assigned U.S. Pat. No. 4,791,151 and are usefullyemployed in accordance with the invention. In all of these cases themajority of the surface area of the particle will be occupied by atleast one outer phase and the interior of the particle will be occupiedby at least one inner phase. The two-staged emulsion-polymerizedaddition polymer particles which are embodied in this invention includefrom 5% to 35% of a film forming polymer and from 65% to 95% of anon-film forming polymer, based on the total volume of the polymers.While the preferred morphology is presumed to have the film formingpolymer on the exterior of the particle the invention is not bound bythis morphological configuration. The only constraint being that thefilm forming polymer aid in providing porous films in accordance withthe invention. In certain instances this constraint can be relaxed ifthe multistage particles are blended with a film forming polymer, suchas described in the first embodiment. Preferred diameters ofmulti-staged emulsion-polymerized addition polymer particles range from30 nanometers to 10000 nanometers.

The emulsion polymerization techniques used to prepare such dispersionsare well known in the art such as, for example, U.S. Pat. Nos.4,325,856; 4,654,397; and 4,814,373 and are usefully employed inaccordance with the invention.

If desired, the composition may comprise a physical blend of particlesof single or multi-stage latex copolymers and a polyurethane dispersion.The blend comprises from 0 percent to 100 percent by volume of thesingle or multi-stage copolymers and 100 percent to 0 percent by volumeof polyurethane dispersion particles. All the weight percentages arebased on the total volume of the polymer particles. In a preferredembodiment, the single or multi-staged copolymers are substantiallynon-film forming and range from 65% to 95% by volume. The polyurethanedispersion particles are film forming and range from 5% to 35% byvolume.

The diameters of the polymer particles were measured by using aBrookhaven Model BI-90 Particle Sizer supplied by Brookhaven InstrumentsCorporation, Holtsville, N.Y., which employs a quasi-elastic lightscattering technique to measure the size of the polymer particles. Theintensity of the scattering is a function of particle size. The diameterbased on an intensity weighted average is used. This technique isdescribed in Chapter 3, pages 48-61, entitled Uses and Abuses of PhotonCorrelation Spectroscopy in Particle Sizing by Weiner et al. in 1987edition of American Chemical Society Symposium series. To measure theparticle diameter, 0.1 to 0.2 grants of a sample of acrylic polymer wasdiluted to a total of 40 ml with distilled water. A 2 ml portion wasdelivered into an acrylic cell, which was then capped. The particle sizewas measured for 1000 cycles. The measurement was repeated three timesand an average was reported. The aqueous composition in coating (ii) maycomprise at least two mutually incompatible copolymers, at least one ofwhich is the film forming latex polymer described above.

With regard to the third aspect of the invention the non-film formingpolymer can include large dimension emulsion polymer particles, whichare prepared according to U.S. Pat. No. 5,369,163. The large dimensionemulsion polymer particles are intended to be non-film formingmaterials, such that films prepared from them will retain porosity andare usefully employed in accordance with the invention. Large dimensionemulsion particles suitable for the invention can be achieved by makingthe polymers with a Tg substantially above ambient temperature, or byadding a cross-linking agent such as allyl methacrylate,multi-functional acrylates, or divinyl benzene, at a level adequate tokeep the polymer from film forming in the dry state. Additionally thelarge dimension emulsion polymer particles can be blended with a filmforming polymers.

In accordance with all aspects of the invention, the compositions may beblended with other materials, such as those normally found in paintcompositions and other coating compositions. For example, the copolymermay be blended with a polyurethane, a polyester, a polyamide, an acryliccopolymer, a styrene-acrylic copolymer, polyvinyl alcohol, hydroxyethylcellulose, thickeners, rheology modifiers, additives, fillers,extenders, coalescing aids, platicizers, slip aids, defoamers, glycols,glycerol, biocides, colorants, pigments, or mixtures of these materials,while retaining the film forming and non-film forming properties of theoriginal copolymer blend.

The porous latex films of the present invention can be usefully employedin the preparation of biocatalytic films of immobilized cells ororganisms, such as Escherichia coli. A method for immobilizing viablebut non-growing cell lines of Escherichia coli in highly uniformpatches, the patches consisting of a thin layer of bacteria inacrylate/vinyl acetate copolymer covered with a thin layer of the samecopolymer, devoid of bacteria and sealed at the edges, has been reportedin a publication of Flickinger et al in the Journal of Biotechnology andBioengineering, Vol. 2, pages 45-55 (1999). While the patch coatingmethod is a substantial improvement on a previous method for makinguniformly sealed immobilized cell samples, the authors report that therestill exist major limitations associated with generating immobilizedcell samples that are uniform in thickness and cell content. A principallimitation of the disclosed method, which involves the use of latexfilms, is the inability to control pore size, retarding coalescence ofpores at ambient temperature and retaining permanent pores at elevatedtemperatures. Using a blend of a non-film forming material, for example,a latex emulsion polymer or hydroxyethylcellulose and a latex filmforming polymer a porous polymer film of thickness ranging from 20 to100 μm (wet film thickness) can be prepared that retains an open porestructure from 0° to 120° C. The porous film is drawn out over asterilized stainless steel or polyester sheet and coated with abacterial strain of E. coli. A permeability test is run to confirm thepresence of an open pore structure in the bacteria/latex composite film.The E. coli strain is cultured, grown and studied for biocatalyticactivity at 30° C. Both the permeability test and procedure fordetermining catalytic activity is described in the publication ofFlickinger et al and is usefully employed in accordance with the presentinvention. The inventor's process for preparing the bacteria/latexcomposites has a number of advantages over the patch coat method forpreparing biocatalytic films. The mechanical strength of the latexsupport is significantly improved without compromising viability of thebacterial strain. The porous latex coatings of the present inventionretain their porosity when allowed to dry and do not coalesce at roomtemperature (20-25° C.). Blistering defects associated with the patchcoat method are avoided. The porous films of the present inventionrepresent a substantial improvement of methods for making uniformsamples of immobilized cell/latex composites.

The compositions of the present invention may also be used in coatingprocesses that provide films with unique functional capabilities. Tohave utility, the coating processes would be amenable to forming filmsfrom liquids. Coating processes include liquid spray coating, reverse ordirect roller coating, brush applied coating, slot-die coating, slidecoating, air-knife coating, gravure printing, flexographic printing,wire wound rod coating, or dip coating. All of these coating methods arewell known in the art. Specific embodiments of processes usefullyemployed with the compositions of the invention include:

1. A process for preparing polymeric coatings with low density and thuslow thermal and acoustic conductivity.

2. A process for preparing polymeric membranes which can be used asfilters or size exclusion membranes. Optionally, the polymercompositions of the present invention possess specific chemicalfunctionality to bind or react with other materials. The incorporationof ion exchange materials in the film exemplify such a process.

3. A process for preparing polymeric supports to hold or entraporganisms. Suitable organisms include bacteria, yeast, fungi, plant,algal and mammalian cells. The films are prepared by first mixing thecompositions of the invention with the desired organism and subsequentlycoating this mixture on a suitable substrate using the coating methodsdescribed above. The organism containing films are then utilized inreactors to perform chemical transformations, used as environmentaldetectors, or used for remediation of environmental contaminants.

4. A process for preparing polymeric supports to hold or entrap chemicalcatalysts. The catalyst containing films are then utilized in reactorsto perform chemical transformations.

5. A process for preparing polymeric supports to hold or entraporganisms in order to create viable mixed cultures. By virtue of theirentrapped state, potentially incompatible organisms may be brought in toclose contact with one another without adversely effecting eithermicroorganism population. Mixed cultures containing more than one celltype, induce or enhance production of natural products which may be usedin various applications. The process would be useful, for example, inscreening and production of natural products that may be useful aspharmaceuticals, agricultural chemicals, and industrial chemicals, ormay serve as useful intermediates for such products. The medium orextracts from such mixed cultures can provide a novel source of naturalproducts to screen for biologically-active materials having utility inpharmaceutical, agrochemical or industrial applications. Production fromcells in culture is an established means of obtaining natural products.Such cultures can be manipulated in various ways such as changing thecomposition of the growth medium or culture conditions in order toinduce the production of a desired material or enhance the amountproduced. For example, the polymeric films of the current invention areless susceptible to breakage under conditions of rapid agitation whichis frequently needed to provide adequate aeration of the cultures, canbe stored for longer periods of time while retaining cell viability, canbe used with cells which excrete enzymes capable of degrading alginate,and can be prepared in thin films thus maximizing the efficiency withwhich nutrients and metabolites are exchanged with the surroundingmedium. The entrapped cells may be bacterial, fungal, plant, algal, ormammalian cells, and may be tailored to a given application by priorselection for desired properties or may be genetically-modified toimpart the desired properties. Examples of properties which may bedesirable include the ability to produce a particular product, improvedviability, stability to particular culture conditions such as extreme pHor temperature, or longevity. The mixed culture can comprise two or moreorganisms supplied as entrapped cells in a polymer film. The organismsmay be entrapped in a single film, in different layers of a single film,or in separate films which are subsequently used in the same culture.Alternatively, the mixed culture can contain an organism growing free ina culture medium and one or more additional organisms supplied asentrapped cells in a polymer film. An advantage of supplying one or moreorganisms as entrapped cells in a polymer film is that the entrappedcells, although metabolically active, do not divide and therefore cannotoverwhelm the other organisms in the culture by the ability to grow at afaster rate.

6. A process for preparing polymeric coatings containing encapsulatedmaterials such as biocides; fragrances; herbicides; fungicides; plantgrowth regulators; insecticides; camphor; fertilizers; air freshener;hydrophobic antimicrobial active materials like triclosan, o-phenylphenol; sanitizers; moisturizing creams; skin conditioner oils; UVscreens, or insect repellents. Non-film forming polymers utilized in thecomposition comprise encapsulating polymers as described in U.S. Pat.No. 5,972,363. Advantages of using compositions of the present inventionin such a process are improved small molecule transport properties ascompared materials known in the art.

7. A process for preparing polymeric coatings containing an inorganicnon film forming material, which have absorbed compounds such asbiocides; fragrances; herbicides; fungicides; plant growth regulators;insecticides; camphor; fertilizers; air fresheners; hydrophobicantimicrobial active materials like triclosan, o-phenyl phenol;sanitizers; or insect repellents.

8. A process for preparing polymeric coatings which can be applieddermally wherein the film may contain active ingredients which are meantto transport through film and be delivered transdermally, such as thetransdermal delivery of pharmaceutical agents. The pharmaceutical agentswould be incorporated in non-film forming polymers using methodsdescribed in U.S. Pat. No. 5,972,363. By virtue of their porosity, suchfilms have utility as a breathable patch for skin.

9. A process for preparing polymeric coatings which serve as a templatematrix for the formation of inorganic materials such as metal oxides,conductive materials such as metals, or narrow sized/poroussemiconductor materials, in which the porous polymer film is infusedwith a liquid metal-organic material, such as an organosilicon,organotin, organotitanium, organogermanium, organozirconium, metalalkoxide, or metal chloride materials. The liquid metal-organic materialis allowed to solidify through known reactions with water. If desired,after solidification of the metal-organic material, the coatingcompositions of the invention may removed by thermal degradation orpyrolysis.

10. A process for preparing polymeric coatings which can be used for thefor the separation of gases, or the separation of low boiling pointliquids from solvents such as water.

11. A process for preparing porous polymeric coatings on a substrate,wherein the porous polymer coatings acts to provide anchoring sites forsubsequent coating layers.

12. A process for preparing polymeric coatings which can be site appliedover architectural structures or building construction materials usingthe above coating techniques; wherein the applied coating issubstantially impervious to liquid water but by virtue of its porosityretains substantial permeability to water vapor.

13. A process for preparing polymeric coatings wherein the coatings whenapplied to textiles will reduce the permeability of the textile toliquid water while maintaining permeability to water vapor.

14. A process for preparing water vapor permeable polymeric coatingswherein the coatings when applied to textiles wherein the coatingcomposition contain conductive materials such as conductive carbon blackso as to act as means to reduce static.

15. A process for preparing polymeric coatings wherein the coating areapplied to non-porous substrates such as photo transparencies, and thecoatings make the substrate receptive to ink printing through absorptionand/or specific reactions in the polymeric coating. A preferred use ofthe process is to make ink jet receptive substrates.

16. A printing process utilizing the compositions of the presentinvention as ink binders, wherein the porous compositions provideaccelerated drying speeds. Printing processes comprise flexographicprinting, gravure printing, ink jet printing, and laser printing.

17. A process for preparing polymeric coatings which actively defeatundesirable mildews, fungi, or bacteria; wherein the polymeric coatingscontain embedded organisms which produce bio-active molecules whichinhibit the growth of other microorganisms.

18. A process for preparing polymeric coatings which actively removeformaldehyde from the air in a house by a specific reaction with acomponent in the film. Components in the film include primary amines,hydrazides, or acetyl acetonate.

19. A process for preparing polymeric coatings which act as porousprotective coatings in the manufacture of chemical sensors.

20. A process for preparing polymeric coatings applied to crops whichcontain an agriculturally active compound encapsulated within thenon-film forming polymer.

Some embodiments of the present invention will now be described indetail in the following examples.

EXAMPLES

The abbreviations listed below are used throughout the examples.

BA=Butyl Acrylate

MMA=Methyl Methacrylate

MAA=Methacrylic Acid

nDDM=n.Dodecyl Mercaptan

SLS=Sodium Lauryl Sulfate (28% active)

QM.1458=Heteroalkyl methacrylate.

Polymers 1-4 all prepared by essentially the same process (except thatfor Polymer 1 only a single monomer emulsion was used while for theothers two separate monomer emulsions were used—total feed time is thesame for all four). A detailed description is presented for Polymer 1:

Polymer 1

A 5-liter round-bottom flask equipped with a paddle stirrer,thermocouple, nitrogen inlet, and reflux condenser was charged with amixture of 1070 grams of hot deionized water, 3.0 grams of sodiumpersulfate, and 44 grams of a 100 nm latex seed with a solids content of45%. A monomer emulsion consisting of 425 grams of deionized water, 23.5grams of sodium dodecylbenzene sulfonate (23%), 1728 grams of styrene,36 grams of divinyl benzene, and 36 grams of methacrylic acid wasprepared. Gradual addition of this monomer emulsion was begun as well asgradual addition of 6 grams of sodium persulfate in 180 grams ofdeionized water. The reaction temperature was maintained at 85° C.during the 185 minute addition time for the monomer emulsion and sodiumpersulfate solution. After the gradual additions were complete asolution of 0.015 grams ferrous sulfate heptahydrate in 15 gramsdeionized water was added. A solution of 3.85 grams oftert-butylhydroperoxide (70%) in 80 grams deionized water and a solution5.95 grams isoascorbic acid in 80 grams deionized water were added whilethe temperature was maintained at 85° C. Next, 207 grams of a diluteaqueous sodium hydroxide (1.7%) solution was added. The reaction mixturewas cooled and the product filtered to remove any coagulum formed. Thefinal latex had a solids content of 45.1%, a pH of 5.7, and a particlesize of 348 nm (as measured using a Brookhaven BI-90 instrument).

TABLE 1 Monomer compositions (weights in grams) and properties forPolymers 1-4. Polymer 1 Polymer 2 Polymer 3 Polymer 4 First MonomerEmulsion Water 425 361 319 276 Sodium dodecyl 23.5 20 17.6 15.3 benzenesulfonate (23%) Styrene 1728 1469 1296 1123 Divinylbenzene 36 30.6 2723.4 Methacrylic acid 36 30.6 27 23.4 Second Monomer Emulsion Water 64106 149 Sodium dodecyl 3.5 5.9 8.2 benzene sulfonate (23%) Butylacrylate264.6 441 617.4 Methacrylic acid 5.4 9 12.6 Properties Solids (%) 45.145.3 45.4 45.0 pH 5.7 5.1 4.9 4.9 PS (nm) 348 425 378 414

Polymer 5—Preparation of Emulsion Polymer

A five liter flask was charged with 1461 g deionized water and heated to87° C. while being swept with N₂. A monomer pre-emulsion was preparedfrom 493 g deionized water, 16.1 g SLS, 1350.0 g BA, 75.0 g MMA, 60.0 gMAA, 15.0 g QM.1458 AND 8.6 g nDDM. 120.0 g SLS. 1.9 g ammoniumbicarbonate and 3.74 g ammonium persulfate were added to the flask alongwith 165 g deionized water. The monomer pre-emulsion was then added overtwo hours at 85° C. Over the course of the reaction, 0.82 g ammoniumpersulfate dissolved in 115 g deionized water was also added to theflask in a separate stream. When the addition was complete, the flaskwas cooled and 2.24 g 70% aqueous t-butyl hydroperoxide, 1.12 g sodiumformaldehyde sulfoxylate and a trace of iron sulfate hepta-hydrate wereadded in a total of 45 g deionized water. Rinses were added throughoutthe polymerization. The emulsion polymer had a solids content of 37.2%by weight, a particle size of 50 nm and a pH of 3.1.

Polymer 6—Preparation of Emulsion Polymer

A five liter flask was charged with 1461 g deionized water and heated to87° C. while being swept with N₂. A monomer pre-emulsion was preparedfrom 493 g deionized water, 16.1 g SLS. 750.0 g BA. 660.0 g MMA and 90.0g MAA. 2.0 g SLS. 1.9 g sodium carbonate and 3.74 g ammonium persulfatewere added to the flask along with 165 g deionized water. The monomerpre-emulsion was then added over two hours at 85° C. Over the course ofthe reaction, 0.82 g ammonium persulfate dissolved in 115 g deionizedwater was also added to the flask in a separate stream. When theaddition was complete, the flask was cooled and 2.24 g 70% aqueoust-butyl hydroperoxide, 1.12 g sodium formaldehyde sulfoxylate and atrace of iron sulfate hepta-hydrate were added in a total of 45 gdeionized water. Rinses were added throughout the polymerization. Theemulsion polymer had a solids content of 40.0% by weight, a particlesize of 140 nm and a pH of 4.9.

Polymer 7—Preparation of Emulsion Polymer

A five liter flask was charged with 1700 g deionized water and heated to87° C. while being swept with N₂. A monomer pre-emulsion was preparedfrom 493 g deionized water, 16.1 g SLS, 990.0 g EA, 420.0 g MMA and 90.0g MAA. 2.0 g SLS, 1.9 g sodium carbonate and 3.74 g ammonium persulfatewere added to the flask along with 165 g deionized water. The monomerpre-emulsion was then added over two hours at 85° C. Over the course ofthe reaction, 0.82 g ammonium persulfate dissolved in 115 g deionizedwater was also added to the flask in a separate stream. When theaddition was complete, the flask was cooled and 2.24 g 70% aqueoust-butyl hydroperoxide, 1.12 g sodium formaldehyde sulfoxylate and atrace of iron sulfate hepta-hydrate were added in a total of 45 gdeionized water. Rinses were added throughout the polymerization. Theemulsion polymer had a solids content of 39.5% by weight, a particlesize of 140 nm and a pH of 5.3.

Polymer 8—Preparation of Emulsion Polymer

A five liter flask was charged with 1500 g deionized water and heated to87° C. while being swept with N₂. A monomer pre-emulsion was preparedfrom 493 g deionized water, 16.1 g SLS, 990.0 g EA, 490.5 g MMA and 19.5g MAA. 37.5 g SLS and 3.74 g ammonium persulfate were added to the flaskalong with 120 g deionized water. The monomer pre-emulsion was thenadded over two hours at 85° C. Over the course of the reaction, 2.11 gammonium persulfate dissolved in 115 g deionized water was also added tothe flask in a separate stream. When the addition was complete, theflask was cooled and 2.24 g 70% aqueous t-butyl hydroperoxide, 1.12 gsodium formaldehyde sulfoxylate and a trace of iron sulfatehepta-hydrate were added in a total of 45 g deionized water. Rinses wereadded throughout the polymerization. The emulsion polymer had a solidscontent of 38.8% by weight, a particle size of 60 nm and a pH of 2.1.

Polymer 9—Preparation of Emulsion Polymer

A five liter flask was charged with 1461 g deionized water and heated to87° C. while being swept with N₂. A monomer pre-emulsion was preparedfrom 493 g deionized water, 16.1 g SLS, 1050.0 g BA, 375.0 g MMA, 60 gMAA, 15.0 g QM.1458 AND 8.6 nDDM. 120.0 g SLS, 1.9 ammonium bicarbonateand 3.74 g ammonium persulfate were added to the flask along with 165 gdeionized water. The monomer pre-emulsion was then added over two hoursat 85° C. Over the course of the reaction, 0.82 g ammonium persulfatedissolved in 115 g deionized water was also added to the flask in aseparate stream. When the addition was complete, the flask was cooledand 2.24 g 70% aqueous t-butyl hydroperoxide, 1.12 g sodium formaldehydesulfoxylate and a trace of iron sulfate hepta-hydrate were added in atotal of 45 g deionized water. Rinses were added throughout thepolymerization. The emulsion polymer had a solids content of 38.3% byweight, a particle size of 53 nm and a pH of 7.3.

Polymer 10 Preparation of a Large Dimension Emulsion Polymer

A 5 liter, four-necked flask equipped with a mechanical stirrer,nitrogen sparge, thermocouple and condenser was charged with 208 gramsof water and 0.01 grams of Alipal CO.436. The kettle solution was heatedat 85° C. To the kettle was then added 0.6 grams of butyl acrylate, 0.3grams of methyl methacrylate, 0.3 grams of hydroxyethyl methacrylate,0.8 grams of methacrylic acid, and 0.08 grams of n.dodecanethiol. Fiveminutes later, a kettle initiator, 0.4 grams of APS dissolved in 20grams of water was added. Fifteen minutes later, a monomer emulsioncontaining 19.4 grams of butyl acrylate, 7.3 grams of methylmethacrylate, 7.3 grams of hydroxyethyl methacrylate, 23.2 grams ofmethacrylic acid, 2.52 grams of n.dodecanethiol, and 0.6 grams of AlipalCO.436 in 250 grams of water, and an initiator solution, 0.6 grams APSdissolved in 30 grams of water, were cofed over a period of one hourwhile the kettle temperature was maintained at 85° C. The kettletemperature was held at 85° C. for fifteen minutes after the end of thefeeds.

To the above emulsion polymer was then added 45 grams oftriethanolamine, 9.6 grams decanol, and a mixture of 10 grams of ferroussulfate solution (0.1% active) and 10 grams of versene solution (1%active). Subsequently, three feed, one a monomer emulsion containing 300grams of water, 6.5 grams of Conco AAS.60S (60% active), 200 grams ofbutyl acrylate, 300 grams of styrene, and 0.5 grams of n-dodecanethiol,the second an initiator, 1.5 grams of TBHP and 1.5 grams APS dissolvedin 50 grams of water, and the third a reducing agent, 2 grams of sodiumbisulfite dissolved in 50 grams of water co-fed into the kettle over aperiod of one hour while the kettle temperature was maintained at 85° C.Fifteen minutes after the end of the feed, the kettle was cooled to 63°C. A chaser couple, 1.0 grams of TBHP in 5 grams of water and 0.7 gramsof Formopon in 10 grams of water were added thereafter. Fifteen minuteslater, the polymer was cooled to ambient temperature. The resultingpolymer had 35.5% of total solids and rod-shaped particles 1 microns indiameter, 20-60 microns in length.

Latex Polymer parameters: Polymer ID Particle size (nm) Tg (Calc Fox °C.)  1 348   100  2 425 100/−50  3 378 100/−50  4 414 100/−50  5  50 −43  6 140    6  7 140    12  8  60    10  9  53  −21 10 NA

Example Preparation Example 1

Use Polymer 1 as Supplied (Comparative Example)

Example 2

Use Polymer 2 as Supplied

Example 3

Use Polymer 3 as Supplied

Example 4

Use Polymer 4 as Supplied

Example 5

Blend Polymer 1 with Polymer 5 at a Ratio of 95/5 Polymer 1/Polymer 5Based on Dry Polymer Volume

Example 6

Blend Polymer 1 with Polymer 5 at a Ratio of 85/15 Polymer 1/Polymer 5Based on Dry Polymer Volume

Example 7

Blend Polymer 1 with Polymer 5 at a Ratio of 65/35 Polymer 1/Polymer 5Based on Dry Polymer Volume

Example 8

Blend Polymer 1 with Polymer 5 at a Ratio of 50/50 Polymer 1/Polymer 5Based on Dry Polymer Volume

Example 9

Blend Polymer 1 with Polymer 6 at a Ratio of 95/5 Polymer 1/Polymer 6Based on Dry Polymer Volume

Example 10

Blend Polymer 1 with Polymer 7 at a Ratio of 95/5 Polymer 1/Polymer 7Based on Dry Polymer Volume

Example 11

Blend Polymer 1 with Polymer 8 at a Ratio of 95/5 Polymer 1/Polymer 8Based on Dry Polymer Volume

Example 12

Blend Polymer 1 with Polymer 9 at a Ratio of 95/5 Polymer 1/Polymer 9Based on Dry Polymer Volume

Example 13

Polymer 10 as Supplied.

Test Methods

The aqueous latex dispersion or latex dispersion blend was drawn down at75 microns wet and allowed to dry at ambient temperature for 1 hour. Avisual assessment for cracking was done as well as a finger abrasiontest to determine if the film was friable. It is desirable for the filmto have no cracks and not be friable. Film opacity was used to judgewhether the film was porous. If the film dried to give an opaque filmthen it was deemed to be porous. At that point a few drops of Isopar™ Lwas placed on the film. If the film went from opaque to clear within a10 minute time period, the film was deemed to have an open porousstructure.

Results for Multiphase Polymers Example ID Cracking Friable OpacityIsopar L test 1 Severe very friable opaque goes clear (comparative)cracking 2 no cracking friable opaque goes clear 3 no cracking notfriable opaque goes clear 4 no cracking not friable opaque goes clear

The results show that without a soft film forming polymer phase the hardpolymer forms a porous film, but is quite brittle and friable. Byputting 35 to 15% by volume of a soft polymer on the hard polymer, theresulting film retains porosity and becomes non-friable.

Results for Polymer blends Example ID Cracking Friable Opacity Isopar Ltest 1 Severe very friable opaque goes clear (comparative) cracking 5 nocracking not friable opaque goes clear 6 no cracking not friable opaquegoes clear 7 no cracking not friable opaque goes clear 8 no cracking notfriable translucent stays opaque (comparative)

The results show that by blending between 5 and 35% of a soft/small filmforming binder into the hard polymer the resulting film retains porosityand becomes non friable. At a level of 50% film forming binder the filmlosses its porosity. In a European publication, EP 0 288,203 B1, aprocess is disclosed wherein a 50:50 blend of a hard polymer latex and asoft polymer latex were used in conjunction with a flocculant to producea porous film. The results of comparative Example 8 in the presentapplication show that in the absence of a flocculant, a 50:50 blend of ahard polymer latex and a soft polymer latex does not form a porous film.The results show that it is possible to obtain porous films without theaid of a flocculant if the soft film forming binder is between 5% and35% of the volume of the film. Further, the results of the invention areoutside the result disclosed in EP 0 288,203 B1. The film of example 5was placed in an 80° C. oven for 1 hour, after which the film retainedopacity, and went clear with the Isopar L, thus indicating that the filmretains porosity even at elevated temperature.

Results of polymer blends (different Tgs) Example ID Cracking FriableOpacity Isopar L test  1 Severe very friable opaque goes clear(comparative) cracking  5 no cracking not friable opaque goes clear  9cracking friable opaque goes clear 10 cracking friable opaque goes clear11 cracking friable opaque goes clear 12 no cracking not friable opaquegoes clear 13 no cracking not friable opaque goes clear

The results of example 1, 5, and 9-12 how that polymer Tg and particlesize are important for achieving a porous crack free and non friablefilm. Examples 9-11 all utilize a small film forming binder with a Tgabove 0° C., and all of these crack. Whereas, examples 5 and 12 utilizea small (less than 20% of the large non film former) soft (less than 0°C.) film former. Examples 5 and 12 form porous films which are crackfree and non friable. Additionally, Example 13 shows that a film castfrom the large dimension emulsion polymer is porous and non-friable.

We claim:
 1. A porous, non-friable polymer film having a network ofpores or channels throughout comprising: a blend of (a) at least onesqueous latex dispersion of polymer particles that are non-film forming;and (b) at least one aqueous latex dispersion of polymer particles thatare film forming, wherein polymer particles of (b) have diameters smallenough to fit into interstices formed between polymer particles of (a)and wherein the film forming polymer particles are present in the blendin an amount from between 5 and 35%, based on the total volume of (a)and (b).
 2. The porous, non-friable polymer film according to claim 1,wherein the film forming polymer particles have a Tg not greater than 20C. and the non-film forming polymer particles have a Tg of at least 30C.
 3. The porous, non-friable polymer film according to claim 1, whereinthe non-film forming polymer particles are prepared from acrylicpolymers.
 4. The porous, non-friable polymer film according to claim 1,wherein the film forming latex polymer particles have particle diameters20% or less in size than particle diameters of the non-film formingpolymer particles.
 5. The porous, non-friable polymer film according toclaim 1, wherein the polymer film maintains porosity up to 160° C.